Sub-theme
4. Supporting Aquatic Ecosystem Health and Functions
Topic
4-3. Protection and management of major rivers and lakes, from headwaters to estuaries
Body
The Three Gorges Reservoir is one of the largest hydropower projects around the world which greatly alters the ecological function of the original ecosystem. The riparian zone of The Three Gorges Reservoir is subject to a frequent fluctuation of water level, leading to severe nitrogen loss by leaching. Cyndon dactylon, a perennial stress tolerant plant, is one of the dominant plant species in the riparian zone of The Three Gorges Reservoir. The underlying mechanism that C. dactylon can survive the nitrogen limitation has been under debate. Therefore, this study proposes a scientific hypothesis that the plant communities in the water level fluctuation zone of the TGR may increase the abundance of nitrogen-fixing bacteria in vivo to overcome the long-term flooding. We selected the most dominant plant, C. dactylon in different riparian zones on the Daning River of the TGR to test this hypothesis. We chose a riparian zone along the Daning River, a first-class tributary on the left bank of the TGR in ChinaIn this study, we sampled the plant tissues of C. dactylon and the surrounding soils across different water levels and seasons in the riparian zone of The Three Gorges Reservoir to explore the possible strategy for them to mining nitrogen. Our study found that the C. dactylon in the TGR riparian zone had endophytic nitrogen-fixing bacteria, particularly enriched in the plant foliage. The abundance of endophytic nitrogen-fixing bacteria was significantly negatively correlated with soil ammonia, nitrate, and organic matter, and significantly positively correlated with total phosphorous and moisture content. The endophytic nitrogen-fixing bacteria in C. dactylon were highly diverse, with Proteobacteria as the main dominant genera. The mutual cooperation mode among bacterial species made the endophytic nitrogen-fixing bacteria community of C. dactylon more resilient to environmental pressure, thus more readily adapting to conditions of repeated long-term flooding in the riparian zone of the The Three Gorges Reservoir.